Catheter-guidewire systems of many different types are used in a wide variety of medical procedures. Some of the many types of catheter-guidewire systems are angioscopic catheter systems, angioplasty catheter systems, genito-urinary catheter systems, laser catheter systems and delivery catheter systems; some are intended for diagnostic purposes, and some for therapeutic purposes including balloon dilatation and the delivery of appliances, drugs, contrast media or other useful fluids to internal bodily vessels.
These catheters contain features both favorable and unfavorable in terms of their utility, functionality and versatility. Many of these features can most easily be understood by examination of a single class of guidewire-directed catheter systems--i.e., dilatation balloon catheter-guidewire systems for angioplasty procedures. The following discussion will therefore focus on "exchangeable" angioplasty dilatation balloon catheter-guidewire systems, it being understood that the scope of this disclosure extends well beyond such systems to encompass all guidewire-directed catheter systems and corresponding components. For brevity, the following discussion of the prior art will focus on a comparison of the structural and performance differences between over-the-wire systems in general, and selected single-channel non-over-the-wire systems in particular, with the understanding that the features which distinguish the invention apply as well to multi-channel non-over-the-wire systems in a manner which will be readily apparent to those skilled in the art.
In recent years, angioplasty has gained widespread acceptance and use as a technique for treating atherosclerotic coronary and peripheral vascular diseases. According to this technique, a dilatation balloon catheter-guidewire system is percutaneously introduced into the patient's vasculature under fluoroscopic control until the balloon component of the system spans the confines of a vascular stenosis. Once in position, the balloon is inflated by hydraulic pressure to dilate the stenosis along its length and thereby relieve the obstruction to blood flow created by the stenosis.
The ease or difficulty of properly positioning an angioplasty dilatation balloon catheter-guidewire system inside the vasculature depends on several characteristics of the system, the most prominent being those known in the art as "steerability," "crossing profile" and "pushability."
The term "steerability" denotes the facility with which the course of the catheter-guidewire system can be controlled by the operator during advancement of the system within the confines of the vasculature. In general, the "steerability" of an angioplasty catheter-guidewire system directly depends on the rotational mobility of the guidewire component of the system within the confines of the vasculature. In the typical system, the rotational mobility of the guidewire component relative to the vasculature depends on rotational mobility of the guidewire component relative to the catheter component. Among systems which are otherwise comparable, those with superior steerability are easier to direct into regions of the vasculature requiring treatment.
The term "crossing profile" denotes the cross-sectional profile of the balloon component of the system in its deflated state. Typically, the lower the crossing profile, the less resistance the balloon will provoke and therefore the more readily the system can be advanced through stenotic lesions.
The term "pushability" denotes the degree to which the catheter and guidewire can be advanced into the vasculature without experiencing axial compression. Axial compression is the twisting, gathering or otherwise bending back of any component of the system along the system's longitudinal axis. Axial compression can occur in response to friction from the vasculature or, in the case of percutaneous transluminal coronary angioplasty, in response to friction from the guiding catheter, which is the catheter through which the angioplasty catheter-guidewire system is conducted from the vascular access site (where the system enters the patient's vasculature) to the coronary artery at the location requiring treatment. In general, the pushability of a catheter system varies directly with the axial rigidity of the structural element (typically the guidewire mandrel, catheter body or combination thereof) that provides axial support for the system. Typically, guidewire mandrels provide superior axial support relative to the catheter bodies in prior art catheter-guidewire systems. This circumstance arises because stainless steel is used in the construction of prior art mandrels whereas flexible polymers are commonly used in the construction of catheter bodies. Other things being equal, stainless steel, when rendered into a rod, typically provides superior axial support relative to flexible polymers rendered into thin-waller tubular structures. Hence, systems which rely upon the corresponding guidewire mandrel for support typically offer superior pushability relative to comparable systems which rely upon the corresponding catheter body for axial pushability. Systems that offer the optimal pushability rely upon both the catheter shaft and guidewire mandrel for axial support. Among systems which are otherwise comparable, those with superior pushability are easier to advance within the confines of severe luminal stenoses relative to systems that offer inferior pushability.
Thus, the ease of positioning a catheter system for use varies directly with the "steerability" and "pushability," and inversely with "crossing profile" of the system.
The safety of an angioplasty dilatation balloon catheter-guidewire system depends largely upon the "exchangeability," shaft profile and structural integrity of the system. The term "exchangeability" denotes the ability of the guidewire and the catheter body to be separated while inside the vasculature for purposes of removing one or the other and replacing the removed component with a substitute component which differs in some respect. The need for such an exchange arises when a component originally placed inside the vasculature is discovered subsequent to its placement to be inadequate or inappropriate for a particular stenosis. Systems having the capability of this exchange are termed "exchangeable" or "over-the-wire" systems, and they offer the advantage of allowing one component to be removed and replaced without removal of the other, the exchange thereby taking place without the need to reestablish intraluminal access. This saves time and maintains intraluminal access in the event of inadvertent vessel closure, and in so doing, lowers the risk of patient injury.
Among system which are otherwise comparable, those with lower shaft profiles are safer to use since they provoke less impairment to the surrounding flow of fluid (i.e., blood, blood subsitutes, contrast medium and medications) following installation within the vasculature and are thus less likely to provoke ischemia or to compromise the resolution of intraoperative angiography. In addition, systems with lower shaft profiles can be advanced through lower profile guide catheters and can thus be inserted into the body through smaller incisions. The lower profile thus adds to the safety of these catheters. Other features being equal, single-channel catheters can be constructed with lower shaft profiles relative to multi-channel catheters.
The ease with which a catheter system is prepared for use depends on how easily air can be removed from the system interior and how easily the guidewire component can be installed inside the catheter component. Systems in which air is vented at the distal end are easier to prepare relative to comparable systems that do not have this capability. Systems in which the guidewire is pre-installed (i.e., non-over-the-wire systems) are easier to prepare than systems in which the guidewire is installed by the user (i.e., over-the-wire systems).
Currently, there exist two fundamental types of angioplasty catheter-guidewire systems--over-the-wire systems and non-over-the-wire systems. The distinguishing characteristic which differentiates these two types is the separability, or lack thereof, of the catheter and guidewire components, and hence the exchangeability of the systems. Over-the-wire systems offer certain advantages relative to non-over-the-wire systems. These advantages include separability, which permits one to perform exchange procedures with greater safety, and steerability, which permits one to direct the course of the system within the confines of the vasculature with greater facility. Non-over-the-wire systems on the other hand, particularly single-channel non-over-the-wire systems, offer certain advantages relative to over-the-wire systems. These advantages include superior pushability, crossing profiles and shaft profiles. As a result, non-over-the-wire systems are typically easier to advance across the confines of critical stenoses and less likely to provoke intraoperative ischemia or to compromise the resolution of intraoperative angiography.
The advantages and disadvantages of selected non-over-the wire systems vis-a-vis over-the-wire systems relate, in part, to the practice of bonding the catheter component (and, in particular, the distal balloon component) to the guidewire in the construction of these systems. Samson, W. J., U.S. Pat. No. 4,582,181, Apr. 15, 1986, and Crittenden, J. F., U.S. Pat. No. 4,917,088 , Apr. 17, 1990, describe distinct single-channel non-over-the-wire systems that contain such bonds at the distal catheter-guidewire interface. In these and similar systems, the bond between the balloon and guidewire serves several functions:
(1) It joins the distal aspect of the balloon to the guidewire; PA1 (2) It prevents fluid and gas leakage from the distal aspect of the hydraulic channel and balloon, with the result that systems can be constructed with single channels and thus lower shaft profiles; and PA1 (3) It permits the guidewire to support the balloon against the possibility of axial collapse as the balloon is being advanced through a stenosis, and at the same time confers the axial support of the guidewire to the catheter component, thereby enhancing the pushability of the system as a whole. PA1 (a) use the guidewire assembly to enhance column support of the catheter body during the initial placement of the combination inside the vasulature and across a stenosis; PA1 (b) obtain a pressure-tolerant hydraulic seal for the balloon during use of the balloon in the dilatation of a stenosis; PA1 (c) open the seal to permit the evacuation of air from the distal confines of the catheter during preparation of the catheter with hydraulic fluid (contrast medium) and then close the seal to retain the hydraulic fluid under pressure, thereby circumventing the need to pull a vacuum on the system to remove the air contained within the system during preparation of the device; PA1 (d) open the seal to perfuse a fluid out through the tip of the catheter into the vasculature, and then reclose the seal after the perfusion has been completed, both without removing either the guidewire or the catheter body from the vasculature; PA1 (e) rotate the guidewire relative to the catheter body for purposes of steerability without subjecting either the guidewire or the catheter body to torsional shear; and PA1 (f) disengage the guidewire assembly from the catheter body for purposes of removing either one alone, and re-establish the engagement once a substitute component has been installed.
In short, this bond permits one to construct non-over-the-wire systems with lower shaft profiles and superior pushability relative to over-the-wire systems, which do not contain such bonds and which rely upon the respective catheter bodies for column support. For these and other reasons, this bond is fundamental to the structure and function of most single-channel non-over-the-wire (i.e., fixed-wire and balloon-on-a-wire) devices.
The advantages of the bond are offset, however, by its permanent nature. The permanence of the bond is detrimental in a variety of ways to the structure and function of systems containing such a bond.
First, systems containing such a bond are non-exchangeable which limits the safety of these systems.
Second, the permanence of the bond compromises the steerability of the system. The bond tethers the catheter tube to the guidewire. The catheter tube is substantially larger than the guidewire in cross-sectional profile, and as a result, is more resistant to rotation within a body vessel. By tethering the guidewire to the catheter tube, the bond transmits the rotational resistance of both the catheter tube and the balloon to the guidewire. This in turn limits the ease with which the guidewire can be rotated within a body vessel, thereby compromising the steerability of the entire system.
Third, the permanence of the bond compromises the structural integrity of the system. Torsional stress develops within the catheter and guidewire components in the region of the bond when the guidewire is rotated relative to the catheter tube. If this stress is great enough, it can produce tears within the balloon component and fractures within the guidewire component of the system. The bond eliminates any possibility of relief of this stress upon continued rotation of the guidewire in one direction.
In summary, the bond between the balloon and the guidewire confers advantages in terms of shaft profile and pushability, and disadvantages in terms of exchangeability, steerability and structural integrity. The advantages stem from (1) the fact that the system can be constructed with a single channel, and (2) the ability of the system to derive axial support from both the catheter and the guidewire. The disadvantages stem from the permanence of the bond.
As a result of the above considerations, the operator is currently required to choose between over-the-wire systems that offer advantages in terms of exchangeability and steerability, and non-over-the-wire systems that offer advantages in terms of pushability, shaft profile and crossing profile. From the foregoing, it can be appreciated that there exists a continuing need for catheter-guidewire systems which offer exchangeability and steerability commensurate with over-the-wire systems of the prior art, and shaft profile and pushability commensurate with certain non-over-the-wire systems of the prior art which derive column support from the guidewire rather than the catheter body. These and other needs are met by the present invention.